I'm experiencing a rich exhaust odor, it smells like I'm exhausting raw fuel. I have a 302 with a mild thumper cam, 650 edelbrock carb and a single plain performer intake. Ive adjusted my air mixture screws by running them in till rough idle then backing out until smooth. I called edelbrock tech support and one tech said that's the nature of the thumper cam and recommended I adjust my timing, can't remember to what degree, I think 14btdc. My plugs look to be burning normal with no signs of fouling or black build up, the tailpipes do have black build up inside. I called back to see if I could get info/advise on smaller jets and got a different tech. I had to go over all symptoms again and this tech said I needed a 3 circuit Holly. He said edelbrock made only a 2 circuit and going to smaller jets would be a loss of power on low and high end. The car runs good, does not overheat, pulls strong but does stumble a little on initial acceleration when at normal temp. I just insulated my fuel line be in case the manifold heat is affecting my fuel line temperature but no change. Has anyone experienced these symptoms or heard of the difference between a 2 or 3 circuit carb. I was surprised to hear a edelbrock tech recommend a Holly carb but willing to try one if I can't figure current configuration out.
It's very hard to "read" plugs on unleaded gas.
I'd try to a-b another known good carb first.
Goodluck,
Ron.
I think it's the cam. A cam with a lot of overlap allows intake air to go directly to the exhaust when the cam is in the "overlap" position. The problem only presents itself at idle, at higher speeds there isn't time for that to happen. Thumper type cams usually have a lot of overlap, that's what makes them thump. John
I did not think about the issues with unleaded gas and plug burning indicators. I pulled the plugs thinking I'd see indications of rich burn. It does seem to be at idle only. I thought about a hotter plug but after reading some on that I'm afraid of damaging something internal. My thought is to try another carb just to see if a Holley makes a difference but not sure if a 600cfm is a good size for the 302. Any suggestions as to whether I should try another 600 cfm or go to a 500 cfm. I put the data in the Holley website chart and it looks as though I could stay with the 600cfm. Other than the performer intake, headers, and cam the rest is close to stock, no special heads or pistons etc. Thank you gentlemen for your feedback.
600 would be good for the 302.
Check manifold vacuum first. I would set timing at 12 btdc, adjust the idle screws for max vacuum. Drive listening for ping, if non bump the timing up 2 and drive again after repeating the vacuum check.
The power valve will have numbers cast on the side of one of the flats. It should be higher then your vacuum reads with the "tune" set correctly. If it is lower or close to the same go to the Holley site and get a new valve that is 2 points higher then the vacuum reading.
Have you checked the float level ? That can make them a bit stinky if it's set to high.
I had a bad brass float and corrected that, this is the second edelbrock float I've had go bad. I'm going to try the vacuum gauge and adjustments, if that doesn't correct it I'll order a Holley and try that. Thanks for your replies.
If you are buying a new Holley get one with annular boosters. Small cfm too. Stock 302's used
about 400-500 cfm.
You have a low torque engine with a higher rpm cam and intake in a fairly heavy car. Not especially good
for a cruiser. A small carb will crutch it somewhat.
Goodluck,
Ron.
So Ron your validating my second thoughts about putting in a 302. I really wanted to go with a 351 or a 390 but I had this 302 with money in it and thought it would be ok, since I'm not a young buck anymore and don't need to smoke the tires.
All joking aside I did read on this forum where a few folks had installed 302's, I discussed the power and cruise ability with an engine rebuild shop that has done a few engines for me that made me feel it would be ok. I am pleased with the 0-60 and general cruising abilities. I am looking at buying a different rear gear ring and pinion since I have an AOD tranny, it could use a lower ratio which will help some. It's not a race car by any means but it doesn't seem to be struggling at all to merge with hiway traffic and cruise at hiway speeds. I'm pleased with the drivability overall, if I were to do it over again I'd be going with a few more cubic inches.
I've been googling Holley carbs and prices in preparation of buying one. I will be playing with adjustment to what I currently have, I'm going to put the vacuum gauge on it today and see where I go from there. Thanks again for the advice and recommendations.
If it were mine I'd be swapping out that Thumpr cam for something a little more mild, like one from their Energy series to get some mid-range power back. Those Thumpr cams usually require higher stall converters, lower rear gears, more compression, other wise the engine can feel a little soggy in the bottom end.
It's a mild thumper cam, I think th mutha thumper is the more aggressive cam. This one is fairly close to an rv cam. Just enough to perk up that 302.
Mutha Thumpr (middle of the three COMP Thumpr series...Thumpr, Muthr Thumpr, Big Muthr Thumpr) roller version in 351 with 1.7 roller rockers. 8+:1 CR. 2500 RPM stall (hardly different than OEM convertor). Modified AOD with wide ratio gear set. 3.00 gear to be changed to 3.89 this winter. Good torque...easily does burn outs and barks the tires in second gear even with the 3.00 gear but needs rear end control really bad. I'm building Traction Master style bars now.
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